1. Field of the Invention
The present invention relates generally to electrical wiring devices, and particularly to protective wiring devices.
2. Technical Background
AC power is provided to a house, building or other such facilities by coupling one or more breaker panels to an electrical distribution system, or another such source of AC power. The breaker panel distributes AC power to one or more branch electric circuits installed in the structure. The electric circuits typically include one or more receptacle outlets and may further transmit AC power to one or more electrically powered devices, commonly referred to in the art as load circuits. The receptacle outlets provide power to user-accessible loads that include a power cord and plug, with the plug being insertable into the receptacle outlet. Because certain types of faults have been known to occur in electrical wiring systems, each electric circuit typically employs one or more electric circuit protection devices. Electric circuit protective devices have been disposed within the breaker panel, receptacle outlets, plugs and the like.
Both receptacle wiring devices and electric circuit protective wiring devices in general, are disposed in an electrically non-conductive housing. The housing includes electrical terminals that are electrically insulated from each other. The line terminals are intended to be connected by the installer to a power source of an electrical distribution system, and the feed-through load terminals are intended to be connected to provide the electrical power to downstream receptacles, lighting fixtures, switches, and the like. Receptacle load terminals are electrically connected to the feed-through load terminals. The receptacle load terminals are configured to align with the blades of an attachment plug in order to provide source power by way of the plug to a user attachable load. Protective devices typically include a circuit interrupter that connects the line terminals to the load terminals in the reset state and disconnects the line terminals from the feed-through and receptacle load terminals in the tripped state. The circuit interrupter trips when a fault condition occurs. There are various types of protective devices including ground fault circuit interrupters (GFCIs), ground-fault equipment protectors (GFEPs), and arc fault circuit interrupters (AFCIs). Some protective devices include both GFCIs and AFCIs.
An arc fault typically manifests itself as a high frequency current signal. Accordingly, an AFCI may be configured to detect various high frequency signals and de-energize the electrical circuit in response thereto. A ground fault occurs when a current carrying (hot) conductor creates an unintended current path to ground. A differential current is created between the hot/neutral conductors because some of the current flowing in the circuit is diverted into the unintended current path. The unintended current path represents an electrical shock hazard. Ground faults, as well as arc faults, may also result in fire.
A “grounded neutral” is another type of ground fault. This type of fault may occur when the load neutral terminal, or a conductor connected to the load neutral terminal, becomes grounded. While this condition does not represent an immediate shock hazard, it may lead to serious hazard. As noted above, a GFCI will trip under normal conditions when the differential current is greater than or equal to approximately 6 mA. However, when the load neutral conductor is grounded the GFCI becomes de-sensitized because some of the return path current is diverted to ground. When this happens, it may take up to 30 mA of differential current before the GFCI trips. Therefore, if a double-fault condition occurs, i.e., if the user comes into contact with a hot conductor (the first fault) when simultaneously contacting a neutral conductor that has been grounded on the load side (the second fault), the user may experience serious injury or death.
Another type of fault condition is commonly referred to as miswiring, or reverse wiring. A protective device may be miswired during installation by connecting the load terminals to AC power. When this happens, the circuit interrupter may be unable to interrupt the flow of electrical current to the receptacle terminals when a fault condition is present. Unfortunately, protective devices do not typically alert the user to the miswire condition. Thus, it is not until damage or injury occur that the miswired condition is evident. As noted above, receptacle load terminals and the feed-through load terminals may be permanently connected by an electrical conductor. When a device is properly wired, the circuit interrupter typically includes a single breaker that breaks the connection between the line terminals and both the feed-through load terminals and the receptacle load terminals. In other words, the typical protective device is not configured to remove power from the user load when a hazardous fault condition is extant. Accordingly, when a receptacle type device is reverse wired, unprotected AC power may be available at the receptacle load terminals when the circuit interrupter is in the tripped state.
Protective devices may be equipped with a test button. However, while test buttons may be determine the ability of the protective device to detect and interrupt a fault condition, they are typically not configured to reveal a reverse-wired condition. Accordingly, many devices are provided with wiring instruction sheets. Unfortunately, instruction sheets are often ignored by installers.
In one approach that has been considered, a protective device is equipped with a barrier(s) that is/are configured to prevent circuit reset until AC voltage is present at the line terminals. The barrier may alert the installer to the reverse-wired condition by preventing reset of the device and by denying AC power to the feed-through load. This approach may be effective during the original installation of the protective device. However, once proper installation is effected the barrier is deactivated and inoperative during a subsequent re-installation. This drawback is further exacerbated by the fact that the installation instructions are unlikely to be available for any re-installation.
In another approach that has been considered, a protective device may be equipped with a fuse that is configured to prevent circuit interrupter reset until AC voltage is provided to the line terminals. The fuse circuit prevents reset of the device and denies power to the feed-through load until proper wiring is effected. Once proper wiring is effected, the fuse blows and is no longer available to detect a reverse-wired condition if there is a reinstallation. Again, making matters worse, the installation instructions are likely to be lost and not available for any re-installation.
In another approach that has been considered, a protective device may be equipped with one or more sets of isolating contacts disposed between the feed-through load terminals and the receptacle load terminals. In this approach, the set of isolating contacts may be controlled by a miswire detection circuit. In the event of a miswire condition, the miswire detection circuit is configured to either open (or prevent closure) of the isolating contacts. After a proper wiring condition is detected, the miswire detection circuit is configured to either close (or permit closure) of the isolating contacts. Like the other approaches considered above, the miswire detection circuit is ineffectual after an initial proper installation, and is no longer available to detect a reverse-wired condition during any reinstallation. Thus, the isolating contacts are closed in spite of a reverse wired condition.
What is needed is a protective device that denies power to the protected circuit, including receptacle terminals, during a miswired condition. Further, a protective device, responsive to the miswired condition during each and every installation, is needed.